According to my husband, the piyut was written by Yehuda ben Shmuel Ibn Abbas (Judah Samuel Ben Abbas), a Spanish poet of the thirteenth century. The topic is the Binding of Isaac, Akedat Yitzchak, which is the Torah reading for the second day of Rosh Hashana.

How we (our family is Ashekanzi through and through) ended up in a Sephardi shul

Jacob da Jew, I added the link explaining how we ended up at Etz Ahaim. And because my husband loves the piyuttim, he pays attention to them. Unfortunately, we don’t own a mahzor, either Ashkenazi or Sephardi, so I am going to try to borrow one to finish this post. At least with typing up the piyut. But that may not happen until next year.

Lorri, I will enjoy reading what you find out.
ID, that’s interesting, you did sing Unatenneh Tokef! I’m taking my husband’s word for it that it is not sung in our shul, as I wasn’t actually in shul all that much (a six-year-old had other ideas).